Thousands of protesters marched through Paris on Sunday against a European fiscal pact, the first major display of public anger to face President Francois Hollande since his May election.

The march organised by the Left Front coalition drew trade unionists, far-left sympathisers and other opponents of the EU accord, two days before lawmakers start to debate a draft law of the budget pact in the lower house of parliament.

The budget discipline pact, which Hollande supports, is expected to pass in both houses of parliament thanks to support from Socialist lawmakers helped by advocates of fiscal discipline in the centre-right opposition.

But the vote has exposed rifts in Hollande's ruling coalition, with far-left allies and Greens planning to vote against it in a challenge to the increasingly unpopular Socialist leader's authority.

If Hollande has to rely on opponents to pass the pact, the vote could deepen the rift in his alliance and embolden left-wing allies seeking a change of course from strict adherence to European deficit targets.

"To him (Hollande), this vote was a formality that simply needed to be rushed through," said Jean-Luc Melenchon, a fiery leftist orator who ranked fourth in an April presidential vote.

"Now he will understand this is not the case, that in France and in the rest of Europe there is an organised opposition to this pact and to all austerity policies."

Wearing his signature red scarf, Melenchon marched at the head of protesters among giant banners bearing slogans such as "Francois Hollande, We Don't Want Your Treaty" and "In Greece and in France, Let's Fight Against Finance".

It was the latest in a series of protests across southern Europe this week as tens of thousands took to streets in Spain, Italy, Greece and Portugal to voice their anger over hardship imposed by austerity policies.

For Hollande, the outcry from many people who voted him into power highlights the difficulty of pleasing a largely left-wing support base even as he shuns painful cuts to welfare programmes.

A 2013 budget unveiled on Friday shaves 30 billion euros off the public deficit, largely through tax increases on big businesses and the wealthy. But it avoids the type of painful austerity measures imposed elsewhere in Europe.

Efforts to preserve the generous public safety net have done little to preserve Hollande's approval rating, which has plummeted since his election, hitting a low of 43 percent in one poll last week.

"This treaty will considerably worsen the situation in the European Union and in France," said one protester, Pierre Khalfa. "We can already see that austerity policies in Europe are leading to recession, so we need to start a movement against these policies, which will lead our country into a wall."

Left Front organisers said some 40,000 people joined the Paris protest. Police declined to provide an estimate.

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